234 DEVELOPMENT OF ELASMOBRANCH FISHES. 



vesicle of an ovum. The whole of the contents of the germinal 

 vesicle become at its disappearance mingled with the proto- 

 plasm of the ovum, but the resistant membrane remains and 

 is eventually ejected from the egg, vide p. 215 et seq. If the 

 remnant of the old nucleus in the cases described is nothing 

 more than its membrane, no difficulty is offered to the view 

 that the constituents of the old nucleus may help to form the 

 new ones. 



In many cases the total bulk of the new nuclei is greater 

 than that of the old one ; in such instances part of the proto- 

 plasm of the cell necessarily has a share in forming the new 

 nuclei. 



Although, in instances where the nucleus vanishes, an abso- 

 lute demonstration of the formation of the fresh nuclei from the 

 matter of the old one is not possible ; yet, if cases of the division 

 of the old nucleus to form the new ones be admitted to exist, 

 the derivation in the first process of the fresh nuclei from the 

 old ones must be postulated in order to maintain a continuity 

 between the two processes of formation ; and, as I have attempted 

 to shew, all the circumstantial evidence is in favour of it. 



Admitting the existence of the two extreme processes of nu- 

 clear formation, I wish to shew that my results in Elasmobranchs 

 tend to demonstrate the existence of intermediate steps between 

 them. The first figures I described of two opposed cones, appear 

 to me almost certainly to represent nuclei in the act of dissolu- 

 tion ; but though a portion of the nucleus may stream out into 

 the yolk, I think it impossible that the whole of it does 1 . 



I described these bodies in two states. An earlier one, in 

 which the two cones were separated by an irregular row of 

 deeply stained granules ; and a later one in which a furrow had 

 already appeared dividing the cones as well as the cell. In 

 neither of these conditions could I see any signs of the body 

 vanishing completely. It was as clearly defined and as deeply 

 stained as an ordinary nucleus, and in its later condition the 

 signs of the streaming out of material from its pointed extremi- 

 ties were less marked than in the earlier stage. 



1 After Strasburger's observation it must be considered very doubtful whether the 

 streaming out of the contents of the nucleus, in the manner implied in the text, really 

 takes place. 



